arXiv subjects

S. K. Singh

Publications and source records attributed to S. K. Singh.

At least 73 records · Page 4Linked to original sources

arXiv2020

Competition between fractional quantum Hall liquid and Wigner solid at small fillings: Role of layer thickness and Landau level mixing

What is the fate of the ground state of a two-dimensional electron system (2DES) at very low Landau level filling factors ($ν$) where interaction reigns supreme? An ordered array of electrons, the so-called Wigner crystal, has long been believed to be the answer. It was in fact the search for the elusive Wigner crystal that led to the discovery of an unexpected, incompressible liquid state, namely the fractional quantum Hall state at $ν=1/3$. Understanding the competition between the liquid and solid ground states has since remained an active field of fundamental research. Here we report experimental data for a new two-dimensional system where the electrons are confined to an AlAs quantum well. The exceptionally high quality of the samples and the large electron effective mass allow us to determine the liquid-solid phase diagram for the two-dimensional electrons in a large range of filling factors near $\simeq 1/3$ and $\simeq 1/5$. The data and their comparison with an available theoretical phase diagram reveal the crucial role of Landau level mixing and finite electron layer thickness in determining the prevailing ground states.

cond-mat.mes-hall↗

arXiv2020

Quasielastic production of polarized $τ$ leptons in $ν_τ$ and $\barν_τ$ scattering from nucleons

The cross sections and polarization components of the $τ$ leptons produced in the charged current induced quasielastic $ν_τ~(\barν_τ) - N$ scattering have been studied. The theoretical uncertainties arising due to the use of different vector form factors and the axial dipole mass in the axial vector form factor have been investigated. Due to the high mass of $τ$ lepton, the contributions from the term containing pseudoscalar and second class current form factors are non-negligible and contribute to the uncertainty in the cross section and polarization observables as these form factors are not well known. In view of the currently proposed experiments by DUNE, SHiP and DsTau collaborations to study the production of $τ$ lepton, an updated calculation of the cross sections and polarizations of tau leptons in the case of quasielastic production have been done and the numerical results have been presented along with a discussion of the theoretical uncertainties.

hep-ph↗

arXiv2020

Nonperturbative and higher order perturbative effects in deep inelastic $ν_τ/\barν_τ-$nucleon scattering

The effect of nonperturbative and higher order perturbative corrections to all the free nucleon structure functions ($F_{iN}(x,Q^2); i=1-5$) in the DIS of $ν_τ/{\barν}_τ$ on nucleon is studied. The target mass correction (TMC) and higher twist (HT) effects are incorporated following the works of Kretzer et al. and Dasgupta et al., respectively. The evaluation of the nucleon structure functions has been performed by using the MMHT 2014 parameterization of the parton distribution functions (PDFs). The calculations have been performed at the next-to-leading(NLO) order. These nucleon structure functions (SF) are used to calculate the DIS cross section by further including the kinematical corrections due to $τ$-lepton mass. Due to the inclusion of lepton mass two additional structure functions $F_{4N}(x,Q^2)$ and $F_{5N}(x,Q^2)$ become non-negligible. The results for the nucleon structure functions, differential and total scattering cross sections are presented. The various effects considered in this work are effective in the different regions of $x$ and $Q^2$, and quite important in the energy region of $E_{ν_τ/{\barν}_τ} < 15$ GeV. A comparative study of our results with the existing results in the literature for the cross sections is made in the energy region of interest for the DUNE, SHiP, DsTau and HyperK experiments proposed to be done in the near future.

hep-ph↗

arXiv2020

Photon induced K$Λ$ production on the proton in the low energy region

The associated photoproduction of $KΛ$ from the proton in the low energy region is studied using an isobar model in which the non-resonant contributions are obtained from the non-linear sigma model with chiral SU(3) symmetry which predicts, in a natural way, the contact term with its coupling strength along with the coupling strengths of the various Born terms predicted by the non-linear sigma model. The present model is an extension of the non-linear sigma model with chiral SU(2) symmetry, used earlier to study the photo, electro, and neutrino productions of pions. In the resonance sector, the contributions from the well established nucleon resonances ($R$) in the $s$ channel, the hyperon resonances ($Y^{*}$) in the $u$ channel, and the kaon resonances ($K^{*}$ and $K_{1}$) in the $t$ channel having spin $\le \frac{3}{2}$ and mass $<2$ GeV with a significant branching ratio in $KΛ$ decay mode, have been considered. The strong and electromagnetic couplings of the $s$ channel nucleon resonances are taken from experiments while the couplings for the resonances in the $t$ and $u$ channels are fitted to reproduce the current data on the associated photoproduction of $KΛ$ in this energy region. The numerical results are presented for the total and differential cross sections and are compared with the available experimental data from CLAS and SAPHIR as well as with some of the recent theoretical models.

hep-ph↗

arXiv2019

Weak structure functions in $ν_l-N$ and $ν_l-A$ scattering with nonperturbative and higher order perturbative QCD effects

We study the effect of various perturbative and nonperturbative QCD corrections on the free nucleon structure functions ($F_{iN}^{WI}(x,Q^2); ~i=1-3$) and their implications in the determination of nuclear structure functions. The evaluation of the nucleon structure functions has been performed by using the MMHT 2014 PDFs parameterization, and the TMC and HT effects are incorporated following the works of Schienbein et al. and Dasgupta et al., respectively. These nucleon structure functions are taken as input in the determination of nuclear structure functions. The numerical calculations for the $ν_l/\barν_l-A$ DIS process have been performed by incorporating the nuclear medium effects like Fermi motion, binding energy, nucleon correlations, mesonic contributions, shadowing and antishadowing in several nuclear targets such as carbon, polystyrene scintillator, iron and lead which are being used in MINERvA, and in argon nucleus which is relevant for the ArgoNeuT and DUNE experiments. The differential scattering cross sections $\frac{d^2σ_A^{WI}}{dx dy}$ and $(\frac{dσ_A^{WI}}{dx}/\frac{dσ_{CH}^{WI}}{dx})$ have also been studied in the kinematic region of MINERvA experiment. The theoretical results are compared with the recent experimental data of MINERvA and the earlier data of NuTeV, CCFR, CDHSW and CHORUS collaborations. Moreover, a comparative analysis of the present results for the ratio $(\frac{dσ_A^{WI}}{dx}/\frac{dσ_{CH}^{WI}}{dx})$, and the results from the MC generator GENIE and other phenomenological models of Bodek and Yang, and Cloet et al., has been performed in the context of MINERvA experiment. The predictions have also been made for $\barν_l-A$ cross section relevant for MINERvA experiment.

hep-ph↗

arXiv2019

Fokker-Planck model for binary mixtures

In dilute gas kinetic theory, model collision dynamics such as Bhatnagar-Gross-Krook (BGK) model is often used to get a better insight and numerical modelling. BGK model and its variants assume that highly nonlinear collision term can be replaced by a simple relaxation dynamics towards Maxwell-Boltzmann distribution. Lebowitz et al., proposed an alternative framework for the collision model, known as Fokker-Planck model, where the relaxation of an arbitrary distribution towards Maxwell-Boltzmann distribution is modelled as a drift-diffusion process in velocity space. In the present manuscript, we extend the single component Fokker-Planck model to a binary gas mixture model over a large range of Schmidt numbers. We prove that these mixture models satisfy the necessary conservation laws and the H-theorem.

cond-mat.stat-mech↗

arXiv2019

Nucleon and nuclear structure functions with non-perturbative and higher order perturbative QCD effects

We have studied the nucleon structure functions $F_{iN}^{EM} (x,Q^2);~i=1,2$, by including contributions due to the higher order perturbative QCD effect up to NNLO and the non-perturbative effects due to the kinematical and dynamical higher twist (HT) effects. The numerical results for $F_{iN}^{EM}(x,Q^2)$ are obtained using Martin, Motylinski, Harland-Lang, Thorne (MMHT) 2014 NLO and NNLO nucleon parton distribution functions (PDFs). The dynamical HT correction has been included following the renormalon approach as well as the phenomenological approach and the kinematical HT effect is incorporated using the works of Schienbein et al. These nucleon structure functions have been used as an input to calculate the nuclear structure functions $F_{iA}^{EM} (x,Q^2)$. In a nucleus, the nuclear corrections arise because of the Fermi motion, binding energy, nucleon correlations, mesonic contribution, shadowing and antishadowing effects. These nuclear corrections are taken into account in the numerical calculations to obtain the nuclear structure functions $F_{iA}^{EM} (x,Q^2)$, for the various nuclear targets like $^{12}C$, $^{27}Al$, $^{56}Fe$, $^{64}Cu$, $^{118}Sn$, $^{197}Au$ and $^{208}Pb$ which are of experimental interest. The effect of isoscalarity correction for nonisoscalar nuclear targets has also been studied. The results for the $F_{iA}^{EM} (x,Q^2)$ are compared with nCTEQ nuclear PDFs parameterization as well as with the experimental results from JLab, SLAC and NMC in the kinematic region of $0.1 \le x \le 0.8$ for several nuclei.

hep-ph↗

arXiv2019

Weak quasielastic hyperon production leading to pions in the antineutrino-nucleus reactions

In this review, we have studied the quasielastic production cross sections and polarization components of $Λ$, $Σ^0$ and $Σ^-$ hyperons induced by the weak charged currents in the antineutrino reactions on the nucleon and the nuclear targets like $^{12}$C, $^{16}$O, $^{40}$Ar and $^{208}$Pb. It is shown that the energy and the $Q^2$ dependence of the cross sections and the various polarization components can be effectively used to determine the axial vector transition form factors in the strangeness sector and test the validity of various symmetry properties of the weak hadronic currents like G-invariance, T-invariance and SU(3) symmetry. In particular, the energy and the $Q^2$ dependence of the polarization components of the hyperons is found to be sensitive enough to determine the presence of the second class current with or without T-invariance. These hyperons decay dominantly into pions giving an additional contribution to the weak pion production induced by the antineutrinos. This contribution is shown to be quantitatively significant as compared to the pion production by the $Δ$ excitation in the nuclear targets in the sub-GeV energy region relevant for the $\barν_μ$ cross section measurements in the oscillation experiments. We have also included a few new results, based on our earlier works, which are in the kinematic region of the present and future (anti)neutrino experiments being done with the accelerator (anti)neutrinos at T2K, MicroBooNE, MiniBooNE, NO$ν$A, MINER$ν$A and DUNE, as well as for the atmospheric (anti)neutrino experiments in this energy region.

hep-ph↗

arXiv2018

Second class currents and T violation in quasielastic neutrino and antineutrino scattering from nucleons

The effect of the second class currents with and without time reversal invariance has been studied in the quasielastic production of nucleons and hyperons induced by neutrinos and antineutrinos from the nucleons. The numerical results are presented for the total scattering cross section~($σ$) as well as for the longitudinal, perpendicular and transverse components of the polarization of the final baryons ($p$, $n$, $Λ$, $Σ^-$, $Σ^0$) and muon produced in the quasielastic (anti)neutrino-nucleon scattering induced by the weak charged current. In the case of the production of $Λ$ hyperon, which is the most suitable candidate for making the polarization measurements, we have also calculated the $Q^2$ dependence of the polarization observables and the differential scattering cross section ($dσ/dQ^2$). The measurement of the polarization observables and their $Q^2$ dependence provides an independent way to determine the nucleon-hyperon transition form factors at high $Q^2$ which can provide tests of the symmetries of the weak hadronic currents like G-invariance, T invariance and SU(3) symmetry.

hep-ph↗

arXiv2018

Polarization observables and T-noninvariance in the weak charged current induced electron proton scattering

In this work, we have studied the total scattering cross section ($σ$), differential scattering cross section ($dσ/dQ^2$) as well as the longitudinal ($P_L(E_e,Q^2)$), perpendicular ($P_P(E_e,Q^2)$), and transverse ($P_T(E_e,Q^2)$) components of the polarization of the final hadron ($n$, $ Λ$ and $Σ^0$) produced in the electron proton scattering induced by the weak charged current. We have not assumed T-invariance which allows the transverse component of the hadron polarization perpendicular to the production plane to be non-zero. The numerical results are presented for all the above observables and their dependence on the axial vector form factor and the weak electric form factor are discussed. The present study enables the determination of the axial vector nucleon-hyperon transition form factors at high $ Q^2$ in the strangeness sector which can provide test of the symmetries of the weak hadronic currents like T-invariance and SU(3) symmetry while assuming the hypothesis of conserved vector current and partial conservation of axial vector current.

hep-ph↗

arXiv2018

Role of Spin, Phonon and Plasmon Dynamics on Ferromagnetism in Cr doped 3C-SiC

The defect induced magnetism has initiated a lot of interest in field of spintronics. In this regard, SiC is a promising material because of its unique properties under extreme conditions. Hence it will be very much interesting to investigate the interaction between defects and itinerant carrier in doped SiC for spintronics application. We report the structural stability and magnetic interaction in Cr doped 3C-SiC synthesized by Thermal Plasma Technique. The EPR spectrum of undoped 3C-SiC shows a sharp resonance line corresponding to $g=2.00$ associated with the defects present in the system. Anomalous temperature evolution tendency of the relative intensity of EPR spectra can be attributed to magnetically correlated defects in the host matrix. For the first time we report the detailed quantitative analysis of X-band and Q-band EPR study in Cr doped 3C-SiC which reveals that Cr can be in multivalent state. The non monotonous variation of Longitudinal Mode (LO) of the Raman spectra has been explained based on the interaction between carriers and surface plasmon using Longitudinal optical plasmon coupling model (LOPC). The carrier density calculated by using LOPC fit with experimental data varies from $1.8\times10^{15}$ to $4.2\times10^{17}$ cm$^{-3}$. Room temperature magnetic measurements exhibit ferromagnetic behavior with non-zero coercivity for all the samples up to 7 T field. We, for the first time, show the Curie temperature to be above 760 K. Quantitative analysis of magnetic interaction validates the applicability of Bound Magnetic Polaron Model (BMP) which probably arises from the exchange interaction of Cr$^{3+}$ ions with related (Si, C) defects. The polaron density estimated from the BMP fit agrees well with the carrier density obtained from the line shape fitting of Raman spectra.

cond-mat.mtrl-sci↗

arXiv2017

Weak quasielastic electroproduction of hyperons with polarization observables

With the availability of high luminosity electron beam at the accelerators, there is now the possibility of studying weak quasielastic hyperon production off the proton, i.e. $e^-p \to ν_e Y(Y=Λ,Σ^0)$, which will enable the determination of the nucleon-hyperon vector and axial-vector transition form factors at high $ Q^2$ in the strangeness sector and provide test of the Cabibbo model, G-invariance, CVC, PCAC hypotheses and SU(3) symmetry. In this work, we have studied the total cross section, differential cross section as well as the longitudinal and perpendicular components of polarization of the final hyperons ($ Λ$ and $Σ^0$ produced in these reactions) and presented numerical results for these observables and their sensitivity to the transition form factors.

hep-ph↗

arXiv2017

Neutrino-nucleus cross-sections at supernova neutrino energies

The inclusive neutrino/antineutrino-induced charged and neutral current reaction cross-sections in $^{12}C$, $^{16}O$, $^{40}Ar$, $^{56}Fe$ and $^{208}Pb$ in the energy region of supernova neutrinos/antineutrinos are studied. The calculations are performed in the local density approximation (LDA) taking into account the effects due to Pauli blocking, Fermi motion and the renormalization of weak transition strengths in the nuclear medium. The effect of Coulomb distortion of the lepton produced in the charged current reactions has also been included. The numerical results for the energy dependence of the cross-section $σ(E)$ as well as the flux averaged cross-section and event rates for the charged lepton production in the case of some supernova neutrino/antineutrino fluxes recently discussed in the literature have been presented. We have also given the flux-averaged angular and energy distributions of the charged leptons corresponding to these fluxes.

nucl-th↗

arXiv2017

Neutrino-nucleus cross sections in $^{12}C$ and $^{40}Ar$ with KDAR neutrinos

High intensity monoenergetic muon neutrinos of energy 236 MeV from kaon decay at rest (KDAR) at the medium energy proton accelerator facilities like J-PARC and Fermilab are proposed to be used for making precision measurements of neutrino-nucleus cross sections in $^{12}C$ and $^{40}Ar$ and perform neutrino oscillation experiments in $ν_μ\to ν_μ$ and $ν_μ\to ν_e$ modes. In view of these developments, we study the theoretical uncertainties arising due to the nuclear medium effects in the neutrino-nucleus cross sections as well as in the angular and energy distributions of the charged leptons produced in the charged current (CC) induced reactions by $ν_μ$ and $ν_e$ in $^{12}C$ and $^{40}Ar$ in the energy region of $E_{ν_e(ν_μ)}<$ 300 MeV. The calculations have been done in a microscopic model using the local density approximation which takes into account the nuclear effects due to the Fermi motion, binding energy and long range correlations. The results are compared with the other calculations available in the literature.

nucl-th↗

arXiv2017

New parameterization of the effective field theory motivated relativistic mean field model

A new parameter set is generated for finite and infinite nuclear system within the effective field theory motivated relativistic mean field (ERMF) formalism. The isovector part of the ERMF model employed in the present study includes the coupling of nucleons to the δ and \r{ho} mesons and the cross-coupling of \r{ho} mesons to the σ and ω mesons. The results for the finite and infinite nuclear systems obtained using our parameter set are in harmony with the available experimental data. We find the maximum mass of the neutron star to be 2.03M\odot? and yet a relatively smaller radius at the canonical mass, 12.69 km, as required by the available data.

nucl-th↗

arXiv2017

Nuclear dependence of $R=\frac{σ_L}{σ_T}$ and Callan-Gross relation in nuclei

The electromagnetic nuclear structure functions $F_{1A} (x,Q^2)$, $F_{2A} (x,Q^2)$ and $F_{LA} (x,Q^2)$ have been calculated using a microscopic model of nucleus to study the nuclear medium effects on the ratio $R_A(x,Q^2)=\frac{σ_{LA} (x,Q^2)}{σ_{TA} (x,Q^2)} = \frac{F_{LA} (x,Q^2)}{2xF_{1A} (x,Q^2)}$ and the Callan-Gross relation(CGR) in nuclei. The nuclear medium effects due to the Fermi motion, binding energy, nucleon correlations, mesonic contribution and shadowing have been taken into account. The theoretical results for the nuclear dependence of $R_{A} (x,Q^2)$ and its impact on CGR have been presented and compared with the available experimental data on the various nuclear targets. The predictions have been made for $R_{A} (x,Q^2)$ in the kinematic region of $x$ and $Q^2$ for some nuclei relevant for the future experiments to be performed at the JLab.

hep-ph↗

arXiv2017

Physics Potential of the ICAL detector at the India-based Neutrino Observatory (INO)

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.

physics.ins-det↗

arXiv2017

Recent status of the understanding of neutrino-nucleus cross section

In this work we have presented current understanding of neutrino-nucleon/nucleus cross sections in the few GeV energy region relevant for a precise determination of neutrino oscillation parameters and CP violation in the leptonic sector. In this energy region various processes like quasielastic and inelastic production of single and multipion production, coherent pion production, kaon, eta, hyperon production, associated particle production as well as deep inelastic scattering processes contribute to the neutrino event rates.

hep-ph↗